Python Decorators

1) Simple Decorator (Before)

Write a decorator my_decorator that prints:

Before function

before calling the wrapped function.

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2) Simple Decorator (After)

Modify the decorator so it prints:

After function

after calling the wrapped function.

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3) Decorator That Prints Function Name

Write a decorator that prints the name of the function being called.

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4) Decorator to Log Arguments

Write a decorator that prints the arguments passed to the function.

Example:

Calling greet with ('Alice',)

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5) Decorator to Time Execution

Create a decorator that prints how long the wrapped function runs.

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6) Decorator That Modifies Return

Write a decorator that multiplies the return value of a function by 2.

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7) Using Decorator with No Arguments

Apply a decorator to a simple function say_hello() that just prints "Hi!".

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8) Decorator for Greeting

Write a decorator that adds “Good Morning” before the function output.

Example:

Good Morning!
Have a nice day.

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9) Multiple Decorators

Apply two decorators to the same function (e.g., one prints before, one prints after).

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10) Decorator With Parameter

Create a decorator that takes a parameter (like a prefix string) and uses it when printing.

Example:

@prefix_decorator(">>>")

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11) Decorator for Even/Odd Output

Write a decorator that checks if the returned number from a function is even or odd and prints that.

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12) Decorator With Function Metadata

Use functools.wraps in your decorator so the wrapped function keeps its original __name__.

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13) Decorator to Prevent Execution

Write a decorator that prevents the function from running when a global switch disabled = True is set.

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14) Decorator That Repeats Function

Write a decorator that runs the wrapped function 3 times.

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15) Decorator That Modifies Input

Create a decorator that automatically converts all string arguments to uppercase before calling the function.

Example:

greet("alice") → GREET("ALICE")

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16) Decorator to Catch Exceptions

Write a decorator that catches exceptions and prints:

Error occurred!

instead of crashing.

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17) Decorator That Caches Results

Write a simple caching decorator that stores and reuses return values by input args.

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18) Decorator With Conditional Logic

Write a decorator that skips running the function if a passed-in flag is False.

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19) Class Decorator

Create a decorator (as a class with __call__) that prints "Decorated" before function runs.

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20) Decorator Logger to File

Write a decorator that logs the function name and timestamp to a file (log.txt) each time the function is called.

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🧠 Concepts Covered

Concept	Key Idea
Basic decorator syntax	@my_decorator
Decorating with parameters	@decorator(arg)
Nested decorators	stacking @
Modifying behavior	before/after/wrap
preserving metadata	functools.wraps
exception handling & caching	advanced patterns

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🧩 Starter Template

Here’s a minimal decorator you can reuse:

import functools

def my_decorator(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        print("Before function")
        result = func(*args, **kwargs)
        print("After function")
        return result
    return wrapper

Usage:

@my_decorator
def say_hi():
    print("Hi!")

say_hi()

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canvil: 333f6c7d-6876-4f7e-b6ad-1bdb2233f5c1